Soils Science - AgronomySoil ConservationPesticides and Alternatives

Chapter 3

December 2006

"Land, then, is not merely soil; it is a fountain of energy flowing through a circuit of soils, plants, and animals." - Aldo Leopold, A Sand County Almanac, 1949

Physical Properties and Use

Plants - agriculture and forestryBuilding-bearing strength and drainageWaste disposal - good drainage

Functions of Soil

“Allows” water to infiltrate, not runoffStores WaterProvide nutrients for plantsDecompose materials

Recycle nutrients Return carbon dioxide to atmosphere

Store carbon - reduce atmospheric CO2

SOIL

Air 25%

Mineral Matter 45%

Water 25%

Organic Matter 5%

Component definition: Mixture of mineral matter, organic matter, water, and air.

Example:

What is Soil (page 212)NOT DIRT - dirt is a four letter word!Mineral particles - non-living - 45%Organic matter - 5%

bacteria and other microorganisms partially decomposed plants - humus macroinvertebrates

Pore space - 50% air spaces water filled spaces

Soil Formation - “ingredients” (page 211)

1. Parent Material - rocks - raw materials Types of parent material

• Bedrock

• In PA, most is not the bedrock

• Transported materials:

– glaciers

– water (alluvial)

– erosion and gravity (colluvial)

2. Time3. Organic material4. Climate

5. Topography (slope and location on slope)

Variables determining kind of soil (page 211)

Climate affects rate, type of weathering Temperature fluctuation - freezing and thawing water plant roots - physical and release chemicals Chemical reactions: eg limestone running water glaciers

"Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influences of many things and events of the past." - Charles Kellogg, The Soils That Support Us,1956

Soil Color

Color determined by minerals and oxygen availability

Red, yellow, brown hues - good aerationGray or olive - poorly aerated, poor

drainageMottling - seasonable wet; poor drainageOften dependent on parent material

Soil Texture - mineral particles (213)

Relative amounts (%s) of sand, silt, and clay Contrast sizes - chart 213

Affects infiltrationAffects water holding capacity (drainage)Indirectly affects fertility - adhesion ions to

clay“Strength” for building - clay soils not good

Clay

Less than .002 mmHolds waterForms aggregates - provides soil structure -

“sticky”Excess clay - poor drainage and compaction Derived from shalesGood adsorption of ions

Silt

.002 to .05 mmOptimal amount of soil water retention and

soil air circulationThe best soils have between 50% and 70%

silt

Sand

.05 to 2 mm1000 times larger than clayRapid infiltration/low water holding

capacityGood strength for building

Soil Texture Classes

Proportion of sand, silt, clay See page 214

Soil texture triangle

Soil Structure - (215)Aggregates - individual particles are

“glued” together to form larger piecesProvides pores Examples

granular platy massive - eg. very clayey soils

Why different soil structures Result of soil texture classes Result of organic matter

Granular

Platy

Blocky

(Angular)(Subangular)

Wedge

ColumnarPrismatic

Examples of Soil Structure

Organic Content1 to 20%Determines structure - aggregates of soil particlesColor - darker, more organicFertility (chemistry) and pH - high ion exchange

Soil Density

Largely due to soil texture and organic content

Degree of aggregation importantAffected by human useDense soils - high strength, low porosity,

low permeability, poor for plant growth

Soil and WaterInfiltration and porosity

must have pores - “loose” soils Dependent on soil aggregates, which in turn

depend on• soil texture (think of sand vs. clay)

• organic material in soil

Water holding capacity – ability of soil to hold water like a sponge holds water Increased by organic matter Loam has food capacity to hold water

Putting it all together

Summarize the chart on page 216

Soil Profile (216)Soil Horizons - Stratified horizontal layersUsed to classify the soilO: partially decomposed organic materialA: topsoilB: subsoilC: Parent materialBedrock

Classifying and Naming Soils

Age of soilSpecial features (eg. Fragipans)water related characteristicstexturehorizons - types and depthsCounty Soil Surveys -

Soil Conservation Service of USDA

Soil ChemistryFertility - Ion exchange important

nitrogen (nitrates) phosphorus potassium

pH: 6.5 to 7.0 is best ion (nutrient) uptake many add lime (“sweetens” soil) effect of rainfall PA slightly acid soil

What is happening to our land?The “dirty thirties” (219)

abuse of land- intensive, monoculture farming Dust bowl

Every Year - worldwide 7.4 M acres ruined by erosion 4 M acres turned into deserts - removal of

natural vegetation 8 million converted to other uses - development

Response

Soil Conservation Service - 1935 now Natural Resources Conservation Service

County Conservation Districts Assist farmers Monitor soil erosion from:

• developments, highways, effects on waterways

Causes of soil degradation

Water erosion Types of erosion (217)

Wind erosionSalt building up in soil from excessive

irrigationLoss is “slow” but nearly permanent

1 mm year = 25 mm in 25 years 500 years to replace this

Erosion (pages 220 to 222)

Movement of soil by wind or water to new location

Problems caused by erosion Reduced high quality farmland Sedimentation of waterways Smothering of wetlands and coral reefs

Worldwide: 1% of world cropland is lost each year

Soil Erosion

Sheet and rill erosion buried crops at the base of a hill

Sediment loaded runoff from a field

Causes of Sources of Erosion

Causes of erosion – not using BMPs in Agriculture (60 % in U.S.) Construction Logging

Off-road vehicles use

Amounts in U.S.

Many areas exceed replacement limit: max 1mm/yr

50 million boxcars of soil lost per year 500,000 trains, 100 cars long

Agricultural Losses: Account for 60% of impaired river miles in U.S.

Desertification

Causes Natural or human caused local climate change Erosion or salinization of topsoil due to excess

irrigation (severe on 21% of world’s irrigated land)

Land Resources-Developed Countries

Less cultivated land than 100 years ago Why is there much less cultivated land?

Astounding 400% increase in yield per acre Improved crop varieties Fertilizers Pesticides Irrigation

Developing Countries

Many reaching limits of potential croplandLoss of tropical forests

Tropical Soils: fertility rapidly depleted Erosion a BIG problem Negatively affects rivers and offshore coral

reefs

Soil Conservation - Three Basic Approaches

Managing ground coverManaging TopographyReduced Tillage Systems

Providing Ground Cover

Cover cropping (don’t let the soil bear!) – protect soil in the “off-season”

Mulching

strip cropping/ contour farming and grassed waterways

Farming on contour of hill Alternating crops down slope Grassed waterway

Conservation Tillage: Minimum Tillage Systems (223)

Less frequent plowingOnly plow where planting will occurReduces

Erosion Water loss Fertilizer leaching into waterways

Cons: Purchase different equipment May delay planting May require more herbicides (weed killers)

Managing Topography (pg 221-22)Contour plowing (221)Strip-croppingCrop rotation: planting series all year – land

not ever fallowCover crops: grasses or legumesPerennial speciesDon’t farm on steep slopesFarm Act of 1985: made U.S. first major

food producer to make soil conservation a national priority

Conservation tillage

Leaves at least 30% of last years crop residue on soil surface

Preserving FarmlandAccomplished through the purchase of

agricultural conservation easements (also known as the purchase of development rights) on eligible Lehigh County farm properties.

As of June 2005, more than 175 farms totaling over 15,000 acres have been secured with perpetual agricultural conservation easements

Why Preserve Farmland

Pennsylvania's #1 industry, agriculture local supplies of fresh food protect surface and ground water resources air quality wildlife habitat scenic beauty and open space

How do we farm - options

Traditional – small scale, primarily human energy, less yield per acre

High intensity – high use of fertilizers/energy/water “Factory farms” –

OrganicIPM

Feeding the World (232-233)Population growing - primarily in

developing countries about 80 million more each year

More than 800 million lack food - but, now, sufficient food is grown to feed all

Future: about 9 billion by 2050 Will it be possible to provide food and water

for 9 billion mouths?

The “Green Revolution” (235)

Began in the 1970’sTwo key contributors:

High yield “miracle” crop varieties: rice, wheat, corn

Intensive fertilizer use“Miracle strains” rice, wheat, etc.

Green Revolution led to High Intensity Agriculture

Definition: producing high outputs using “High yield” miracle crops AND high inputs of:

Water - irrigation Fertilizers - organic, inorganic Energy - fossil fuels (Energy inputs in lower intensity agriculture: human

and animal) Pesticides - herbicides, insecticides

1900 1930 1960 1990 2020 2050

Year

0.050

0.040

0.030

0.020

0.010Irri

gat

ed a

rea

per

per

son

(h

ecta

res)

Figure 13-18Page 294

2,000

1,500

1,000

500

0

Gra

in p

rod

uct

ion

(mill

ion

s o

f to

ns)

1950 1960 1970 1980 1990 2000 2010

Total World Grain Production

Year

400

350

300

250

150

Per

cap

ita

gra

in p

rod

uct

ion

(kilo

gra

ms

per

per

son

)

1950 1960 1970 1980 1990 2000 2010

World Grain Production per Capita

200

Year

Increase in Meat vs. Plant Based Diets: Fossil Fuel Inputs/Food Outputs

Food Type Kilocalories of fossil fuel input per kilocalorie of protein output

Feed lot beef 20-78

Pigs

Broiler chicken

Rangeland Beef

Sheep

Vegetables

35

22

10

10

2-4

Producing More MeatProducing More Meat

Kilograms of grain needed per kilogram of body weightKilograms of grain needed per kilogram of body weight

Beef cattleBeef cattle 77

PigsPigs 44

ChickenChicken 2.22.2

Fish (catfishor carp)

Fish (catfishor carp) 22

Fig. 13-25 p. 298

Fig. 13-25 p. 298

Biodiversity Loss

Loss and degradation of habitat fromclearing grasslands and forests anddraining wetland

Fish kills from pesticide runoff

Loss of genetic diversity fromreplacing thousands of wild cropstrains with a few monoculture strains

SoilErosion

Loss of fertility

Salinization

Desertification

Environmental problems of high intensity agriculture

Air PollutionGreenhouse gas emissions from fossilFuel issue

Other air pollutants from fossil fuel use

Pollution from pesticide sprays

WaterAquifer depletion

Increased runoff andflooding from land clearedto grow crops

Sediment pollution fromerosion

Fish kills from pesticiderunoff

Surface and groundwaterpollution from pesticidesand fertilizers

Overfertilization of lakesand slow-moving riversfrom runoff of nitrates andphosphates fromfertilizers, livestockwastes, and foodprocessing wastesEnvironmental problems of high

intensity agriculture

Human Health

Nitrates in drinking water

Pesticide residues in drinking water,food, and air

Contamination of drinking andswimming water with disease organismsfrom livestock wastes

Bacterial contamination of meat

Can Green Revolution Continue? How can the world feed another 3 billion hungry

mouths? Is there a limit to continually increasing yield?Environmental reasons for leveling off

Huge use of energy - petroleum soil erosion depletion/pollution water supplies Effects on humans and animals of pesticides and

fertilizers Costs an issue, especially in developing countries

Fertilizers: Organic vs. Inorganic

Video segment: Soil Sustainability – organic and inorganic fertilizers

Soil Fertility

Soil nutrients- chemicals needed by plants from the soil

Source in natural ecosystem decomposition minerals nitrogen fixation from air

Primary nutrients - NPK

Nitrogen -growth of plant leaves (chlorophyll) and stems

Potassium - stem development, fruit and flower formation

Phosphorus - fruit and flower formationSecondary nutrients - Ca, Mg, and SSoil testing - includes above and pH

Synthetic - chemical - fertilizers

Nitrogen - need high input of fossil fuelsPhosphate - phosphate rock, coal, natural gasPotassium - potash - from mines, extracted

from earthSoil quality: if only synthetic fertilizers, ,

organic matter in soil decreases, soil looses structure and ability to hold water

Organic Farming and GardeningNO chemical pesticides or chemical fertilizersOrganic Fertilizers

Made from dead plant materials or other non-chemical stuff Cottonseed meal, blood meal, fish emulsion, manure and

sewage sludge are examples of organic fertilizers. Compost

• kitchen garbage• leaves• grass clippings• manure

Organic Advantages Improve Soil

Increase water-holding capacity of the soil. Improve the physical structure of the soil which allows

more air to get to plant roots. Bacterial and fungal activity increases in the soil.

• Mycorrhizal fungi make other nutrients more available to plants thrive in soil where the organic matter content is high.

Organically derived plant nutrients are slow to leach less likely to contribute to water pollution than synthetic

fertilizers.

Does not use fossil fuels - imitates natural cycles, so unending supply

Food does not contain pesticides

Disadvantages of Organic FertilizersUsually more expensiveRequires more knowledge and researchHarder to obtain in some cases

What do you see advertised on TV?

Pest Control-3.8

BUGS….can’t live without ‘em, but tough to live with ‘em

PestsWhat is a pest?

Why not a problem in a balanced natural ecosystems?

Examples grasshopper - $400 million each year in U.S. Boll weevil and cotton borer Many fungi on fruit trees Trees

• Hemlock wooly adelgid

• Gypsy moth

• Fungi-chestnut blight, dutch elm disease Transmit diseases - malaria, yellow fever, West

Nile virus, heartworm in dogs

What is a pesticide ( table on 251)What is a pesticide?

Rodenticides Herbicides - weedkiller - most used in U.S. Insecticides Fungicides

Some “natural” - derived from plants - rotenone and pyrethrum

First major production of chemical pesticides - during WWII from nerve gases

DDT organophosphates

Pesticide Use in the U.S.Trend in use:

0

5

10

15

20

25

30

1950 1970 1996

Billion $

Where are Pesticides Used - U.S.

Agriculture: 3/4Herbicides: 59% (Figure 12.5, 252)Household application:

12% of pesticides 23% of insecticides

Do you or your family use pesticides? For what reasons?

Chemical Pesticides -Variables(253-255)Variables - important in determining effect

on humans and environment Persistence (stability) in environment

• High: chlorinated hydrocarbons Biomagnification: Chlorinated hydrocarbons Effects on other organisms

• Broad vs. narrow Spectrum Pesticides

• Toxicity to non-target organisms

Pesticides - Their Good SideDisease Control

Malaria: 50 million humans saved Other diseases for which insects vectors

• Bubonic plague and Yellow fever

Often very and quickly effectiveHave in many cases increased food supplies and

lower cost of foodIf used properly relatively safe

newer pesticides safer

Pesticide Problems Evolution in action: “superbugs” – cannot be killed with the pesticide

(253) Broad spectrum vs. narrow spectrum pesticides Effects on non-target species Creating a new pest – by killing off the predators of an insect (255) Bioaccumulation – example is effect of DDT on birds of prey (254) Persistent in environment ; some not biodegradable

Such as DDT – even now found in high concentrations in human mother’s milk (254)

Effects on human health – many unanswered questions here!

Effects on Nontarget Species

Up to 90% of pesticides never reach targetEffects on other insects - honeybeesKilling beneficial predators (both insect and

non-insect) (see next slide)

Creating “New” Pests

Broad spectrum pesticides - eliminated natural predators and parasites that previously kept pest insects in check Examples: ladybugs, parasitic wasps, and

praying mantis What controls insect pests in nature? Yes, the

NATURAL predators that pesticides often kill off!

Creating “Superbugs”: Resistance & ResurganceInsects become resistance: evolution in actionPercentage crops lost to insects increasing! \

Genetic diversity results in pest resurgence Diagram page 253 Pesticide treadmill – more pesticides become

less effective, so use more, and then becomes less effective again, etc. , Etc.

Persistence(253-254)

Define: the length of time the chemical pesticide remains in the environment.

Vary with pesticidesSome pesticides biomagnify in fatty tissue

100% of people in U.S have detectable amounts of DDT or DDE

Some human mother’s milk: could not be sold due to high levels of some pesticides

The DDT Story (pg. 255 & 3.9)

Dichloro-diphenyl-trichloroethane Degradation product DDE

What were the benefits? Great reduction in malaria, yellow-fever

The decline of predatory birds- What happened??

Banned in early 1970’s in developed countries

Effects of some pesticides on Human Health (Pg.260)

Acute (short term) - High dose exposure Farmworkers most susceptible Mostly children (1966: 22,000 reported) Think about your pets and pescticides sprayed on your

lawns!Chronic

Low doses Long time periods Difficult to assess actual health risks Potential hormone disrupters - rat experiments (read

257)• Extrapolation to humans??

How are Humans Exposed - Chronic?How get exposed

food (264)• children may get larger exposure & more

susceptible

• endocrine disrupters

• Nat Academy of Sciences: 4-20,000 cancer per year in U.S.

waterAgent Orange in Vietnam- 2,4 D

(contamination with dioxin) http://www.lewispublishing.com/orange.htm

How are Humans Exposed - Chronic?

How get exposed food (264)

• children may get larger exposure & more susceptible

• endocrine disrupters water

Agent Orange in Vietnam- 2,4 D (contamination with dioxin) http://www.lewispublishing.com/orange.htm

Who “protects” us? (265)What is “tolerance level”

“maximum amount of pesticide residue allowed in or on food or in drinking water” - EPA

• What must be considered– dose

– toxicity

– persistence

– age of people exposed

– most difficult: synergism

Can you reduce your risks?Follow directions when using pesticidesMinimize useBuy and grow organic organicWash all foodsDon’t demand perfection - see The Perfect

Apple (266)

What is Sustainability

Sustainability rests on the principle that we must meet the needs of the present without compromising the ability of future generations to meet their own needs.

What is Sustainability

Sustainability rests on the principle that we must meet the needs of the present without compromising the ability of future generations to meet their own needs.

See 244 and 245

“Sustainable” Agricultural

Organic FarmingIPM

Example of IPM: Attacking the Gypsy Moth

Integrated Pest Management (IPM)In many cases…50 to 90% reduction in pesticide use w/o reducing production

Replacing the Sledgehammer with the Replacing the Sledgehammer with the ScalpelScalpel High Technology/Education are Keys Precision of application of pesticides Mechanical cultivation and bug vacuums

Goal: select a combination of nonchemical methods but where necessary use less harmful and less persistent chemicals for pest control

Alternatives to Current PesticidesResistant plant varietiesDon’t use monoculture (279)Biological Controls

Beneficial insects - (276-280)• parasitic wasps, lady beetles (parasites)

Bacteria that infect specific insects (B.t.) High technology:Computer programs and

careful monitoring - spray at exact time Birth control: Sterilized males released (so

sorry ladies) Phermones- devastate the bugs sex life

Organic Farming and Gardening

Definition No pesticides No inorganic (chemical) fertilizers

Focus on soil “health” Build up humus in soil

Focus on consumers healthFocus on farm workers healthRodale Organic Research Farm

Why not use organic or IPM?

Farmers/gardeners may not have knowledge, skills

Must accept some loss of crops Lower yields Higher cost of production

• BUT, organic foods do sell for more!

Do you (or does your family) try to buy organic foods?

Why or why not?

Genetic Modified Foods

Insert genes into food or other crops Purposes:

Herbicide resistence (roundup resistant soybeans)

Increase vitamin or other nutritional content Create insect resistant crops

Phase 1Make Modified Gene

Identify and extractgene with desired trait

Identify and removeportion of DNAwith desired trait

Remove plasmidfrom DNA of E. coli

Insert extracted DNA(step 2) into plasmid(step3)

Insert modifiedplasmid into E. coli

Grow in tissueculture tomake copies

cell

gene

DNA

Plasmid

E. coliDNA

Geneticallymodifiedplasmid

plasmid

Phase 2Make Transgenic Cell

Transfer plasmidcopies to a carrier

agrobacterium

Agrobacteriuminserts foreignDNA into plantcell to yieldtransgenic cell

Transfer plasmidto surfacemicroscopic metalparticle

Use gene gunto inject DNAinto plant cell

A. tumefaciens(agrobacterium)

Plant cell

Nucleus

Host DNA

Foreign DNA

Phase 3Grow Genetically Engineered Plant

Transgenic cellfrom Phase 2

Cell division oftransgenic cells

Culture cellsto form plantlets

Transgenic plantswith new traits

Problems

Can genes spread to wild species – this could create wild plants that kill insects – and, overall, insects are good!

Potential and unknown effects on human health Note: foods with GMOs are not labeled